Phosphatizing carried on in water has typically provided drawbacks, including sludging and the need for a multi-step operation, to achieve dry coated articles. In an early attempt to overcome such problems, as described in U.S. Pat. No. 2,515,934, from 1 percent to 7 percent of the commercial phosphoric acid 85 percent syrup was used in an organic mixture, rather than in water. Representative of these mixtures was a 50/50 blend of acetone and carbon tetrachloride. With the blend, only a few steps were needed for phosphatizing.
As the use of chlorinated solvents in phosphatizing operations developed, it became recognized, as discussed, for example, in U.S. Pat. No. 3,197,345, that there was a water-based process, also called an "aqueous" method of phosphatizing metal articles, and on the other hand a solvent-based process, which was therein noted as the "dry" process. The latter process typically employed a solution of phosphoric acid in a chlorinated hydrocarbon solvent.
It was early recognized in the U.S. Pat. No. 2,515,934 patent, that the commercial phosphoric acid would introduce a small amount of water into organic phosphatizing compositions. Several techniques were developed to combat this problem, including the use of drying agents. Several of such concepts have been discussed in U.S. Pat. No. 3,338,754. Therein it was emphasized that small amounts of water are detrimental to the phosphate coatings obtained from the non-aqueous phosphatizing solutions.
The phosphatized coatings that were achieved had the drawback of being water sensitive. However, as has been discussed in U.S. Pat. No. 3,475,228, these phosphatized coatings could nevertheless be successfully topcoated with paint compositions based upon the same chlorinated hydrocarbon solvent for the paint as was used in the dry phosphatizing process.
One variation in the prior art efforts involves the addition of a stabilizing agent to a coating bath to prolong the formation of adherent coatings from the bath. In West German Pat. No. 1,222,351, the use of an agent such as dimethyl glyoxime, as a stabilizer, has been shown. The baths, even with stabilizer, are of dubious quality without the use of commercial ethanol. This necessarily introduces a minor amount of water into the coating composition. However, resulting coatings can display deleterious characteristics with topcoats.
In the past several years there has been an increasing interest in water-reducible coatings, spurred on by the advent of pollution requirements and Federal safety and health legislation. It would, therefore, be most desirable to obtain a phosphatized coating, with the advantages of the dry phosphatizing process, and then be able to couple this, through the advantage of a water-insoluble coating, with the subsequent deposition of a water-reducible coating. Further, commercially developed chrome rinse systems and the like for phosphatized coatings have been developed under strong economic forces that have dictated water-based rinse systems. It would thereby be most desirable to integrate a dry phosphatizing process, with a commercially suitable chrome rinse system that can thereafter be followed by an economical and efficient topcoat operation. It would moreover be most particularly desirable to obtain all such features while providing a phosphatized coating having topcoat compatability with a great variety of solvent based topcoats.